The present invention relates to an arrangement for cooling the pistons and cylinder sleeves of pistons/cylinder units of an internal combustion engine. Each piston/cylinder unit has at least one cooling chamber, which is delimited by the piston and the cylinder sleeve of that unit, and also has suitable sealing means, for example piston rings, provided on that end of the piston closest to the combustion chamber. The cooling chamber extends in the circumferential direction of the piston, is provided with means to supply cooling medium thereto and with means to withdraw cooling medium therefrom, and is provided with at least two approximately axially extending guide elements.
With regard to internal combustion engines, it is necessary to keep the heat which is produced during combustion away from the components of the engine, at least to such an extent that these components are not damaged. Thus, it is already customary to cool the thermally highly stressed piston with motor oil, whereas the outer periphery of the cylinder sleeve or barrel is either air cooled or water cooled. The present invention is concerned with combining the cooling of the piston and the cylinder sleeve, so that the overall cooling of the internal combustion engine, as well as its construction, can be improved and simplified
German Offenlegungsschrift No. 25 41 966 discloses a cooling arrangement of this general type. In this known arrangement, the cylinder sleeve and the piston are cooled at the same time by a single cooling medium, with the cooling medium flowing into a cooling chamber disposed between the piston and the cylinder sleeve; the cooling medium cools the cylinder sleeve from within, and is withdrawn through a second opening. In a further embodiment of this known arrangement, the piston is provided on its surface with an annular space. The means for supplying and withdrawing cooling medium are radial bores which are disposed in the cylinder sleeve. In no position of the piston are these radial bores closed off by the piston. The cooling medium flows through the bore in the wall of the cylinder sleeve into the cooling chamber defined by the piston and the wall of the cylinder sleeve. As the piston moves up and down, the cooling medium cools the piston itself, and that portion of the wall of the cylinder sleeve over which the piston passes. In so doing, the cooling medium can furthermore cool the top of the piston via a separate central chamber within the piston. In order to increase the known Shaker effect, axial and also radial guide plates are provided in the cooling chamber for providing particularly good turbulence to the cooling medium. The cooling medium leaves the cooling chamber by means of a second exit bore located in the wall of the cylinder sleeve opposite the inlet bore. In order to make it possible to utilize a cooling medium other than the motor oil of the internal combustion engine, the aforementioned German Offenlegungsschrift further proposes sealing off the piston with piston rings not only at that end facing the combustion engine, but also at that end facing the crank case.
The aforementioned German Offenlegungsschrift No. 25 41 966 furthermore discloses connecting the cooling medium flow for the arrangement for cooling the cylinder sleeve and piston to an overall cooling medium circulation. While the internal combustion engine is being warmed up, the cooling medium flow can be heated, as a result of which the warm cooling medium flow heats the cylinder unit for the purpose of reducing wear.
However, this heretofore known cooling arrangement has the drawback that considerable partial flows of the cooling medium pass along the periphery of the piston directly from the cooling medium inlet to the cooling medium outlet. Furthermore, a second cooling medium flow is guided via a further separate cooling chamber to the top of the piston, where it cools the combustion chamber recess. The heat-absorption capacity of the cooling medium is therefore poorly utilized, because the heat-absorption capacity of one of the partial cooling medium flows is hardly made use of, whereas the heat-absorption capacity of the second partial cooling medium flow is heavily stressed. Furthermore, the cooling medium does not reach, in particular, the upper annular zones of the piston which are provided with the piston rings and are highly thermally stressed, so that these regions are insufficiently cooled.
It is an object of the present invention to provided a cooling arrangement for simultaneously cooling the piston and the cylinder sleeve, with the heat-absorption capacity of the available cooling medium being better utilized, so that the overall cooling of the internal combustion engine is optimized.